The invention relates to a high ratio planetary type traction roller transmission utilizing two planetary transmission stages.
Such high ratio transmissions are needed in large numbers for converting rotary motion from a high speed motor, for example, for low speed, high torque applications. However, various machines utilize various speeds and torques so that, for different applications, different transmissions are required with different sun rollers, different planetary rollers and different traction rings.
The motion transmitting traction surfaces of such transmissions need to be engaged with one another with forces sufficient to transmit the respective torque and, as the torque changes within a transmission from stage to stage, so do the engagement force requirements. One could of course provide for maximum engagement forces for all the traction surfaces but then all the traction surfaces would be exposed to full loads at all times which not only reduces their lives but also reduces transmission efficiency and would require the use of relatively expensive materials for the traction surface areas.
In the arrangement according to U.S. Pat. No. 4,060,010, for example, the traction roller engagement forces are the same for all the stages although the torque at the drive shaft end of the transmission is by far lower than at the output shaft end.
The same can be said for the arrangement shown in U.S. Pat. No. 3,490,311 in which a single engagement cam structure is provided for both main planetary drive structures providing for both the same engagement forces.
It is the principal object of the present invention to provide a two stage planetary type traction roller transmission in which the traction surfaces are subjected essentially only to the forces needed for the transmission of the appropriate torque and wherein, with the same transmission housing and traction ring structures, various transmission ratio planetary and sun rollers may be utilized, thereby providing for easy changeover to different transmission ratios or for a relatively large variety of different ratio transmissions with relatively few parts.